[Bug libfortran/38199] [4.7/4.8/4.9 Regression] missed optimization: I/O performance

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38199

--- Comment #35 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> http://gcc.gnu.org/ml/fortran/2014-03/msg00079.html

The test

      character buffer*100000
      integer i,j

      DO j=1,9999
        write(buffer,'(i4)') j
        read(buffer,'(i100000)') i
      ENDDO
      end

takes ~3.5s without the patch (and 4.7.4 or 4.8.3) and ~0.7s with it (~2s with
4.6). The test

      character buffer(1)*100000
      integer i,j

      DO j=1,9999
        write(buffer(1),'(i4)') j
        read(buffer,*) i
      ENDDO
      end

takes ~1.8s with/without the patch (~11.3s with 4.6, ~10.2s with 4.7.4, and
~13.6 with 4.8.3, i7 2.8Ghz, turbo 3.8Ghz).